Counterweighted Active Tracking Solar Panel Rack

ABSTRACT

Embodiments of the present invention relate generally to methods and systems for an active tracking solar panel racks.

This application claims priority under 35 U.S.C. § 119 to Provisional Patent Application No. 60/031,868 entitled: “Counterweighted Active Tracking Solar Panel Rack,” filed on Feb. 27, 2008, the disclosures of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to methods and systems for active tracking solar panel racks.

DESCRIPTION OF RELATED ART

One obstacle in roof-top tracking of solar panels involves the uneven distribution of wind forces inherent to the rigidly connected actuator design.

The description herein of disadvantages and deleterious properties associated with known compositions, methods, and systems is in no way intended to limit the scope of the invention to their exclusion. Indeed, embodiments of the invention may include portions of, or one or more known compositions, methods, and systems without suffering from the disadvantages and deleterious properties.

SUMMARY OF THE EMBODIMENTS

One embodiment of the invention encompasses a counterweighted active tracking solar panel rack.

Other objects, features, and characteristics of the present invention will become apparent upon consideration of the following description and the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a single row embodiment.

FIG. 2 shows a side view of the embodiment shown in FIG. 1.

FIG. 3 shows a close up of the mechanical lock assembly of the embodiment shown in FIG. 1.

FIG. 4 shows a close up of the damper assembly of the embodiment shown in FIG. 1.

FIG. 5 shows a close up of the actuator bar of the embodiment shown in FIG 1.

FIG. 6 shows a close up of the actuator bar and the two pulleys that link it to the main cable of the embodiment shown in FIG. 1.

DETAILED DESCRIPTION

Embodiments of this invention include an apparatus that completely decouples the tilt actuator from the wind design constraints and allows the rack to be designed in very much the same way as a fixed rack. Another embodiment of this invention is a method of decoupling tracker mechanism from wind forces on an array. In addition, each driven row is actuated independently through a common drive unit. Embodiments of the invention use ballasts to guarantee an upper load on an actuator system as depicted in the figures. Wind tunnel data is used to provide moments on each row as a function of row panel area, windspeed, and wind direction. The ballast loads are then tuned to provide positive tracking control up to a chosen wind speed at which point the rack is allowed to blow to a mechanically limited stop position. By designing the actuator in this manner, the wind loads are evenly distributed among the array rather than channeled through the actuator system. The actuator system may be designed to 20 mph wind speeds in a 70 mph wind zone for example. This allows design for a force of about 8% which is 20̂2/70̂2.

FIG. 1 is a single row model. One set up has a spacing of ˜10 feet between adjacent rows and the axis down the center of the square tube runs N-S. The “mechanical lock assembly” and “actuator bar” are seen in the center of the picture and the “damper assembly” is seen on the right.

FIG. 2 is a side view of the rack.

FIG. 3 is a close-up of the mechanical lock assembly. Since this rack is designed to “let go” under higher wind speeds (the specific let-go speed is determined in conjunction with the counterweight size), the rack needs a method to constrain the rotation bounds. This unit then transmits all additional force into the local structure providing a distributed roof loading which is very important in a roof-top tracker. It also allows the user to guarantee an upper limit on the actuator loading.

FIG. 4 is the “damper assembly”. An embodiment uses a modified truck shock that has equal damping in both extension and compression. However, since this design only uses extension, any standard car shock, or other shock absorber, without gas pre-load would work.

FIG. 5 is the “actuator bar”. The counterweight on one end provides a constant torque around the rack which will tend to always tilt it to one side. This tendency is countered by the actuator setup that will be described later. An important difference between this approach and a “passive tracker” is that the passive tracker relies on a balanced center of gravity, usually refrigerant that is exposed to the sun. This system is positively controlled and will always have a restoring force equal to the counterweight chosen.

FIG. 6 shows the actuator bar and the two pulleys that link it to the main cable. The way this rack functions is to use a system of two cable types. A main cable runs linearly down the Z channel shown in the photo. This cable will transmit the actuator drive force to each row independently through secondary cables that run through the pulley shown on the end of the actuator bar opposite the counter weight. This cable is then attached to a weight resting on the roof (or protective surface or wear pad). This weight is 2× the counter weight (assuming equal moment arms). The drive of the rack is therefore to always have that weight resting on the roof, but with a tension in the secondary cable equal to that of the counter weight.

Under higher winds, one of two things may happen. 1) With a wind blowing into the page, the rack may pick up this weight sitting on the roof until it reaches a mechanically locked position through the “mechanical lock assembly”. 2) With the wind blowing out from the page, the rack may rotate the rack the other way and introduce some slack into the secondary cable attaching the weight on the roof to the main drive cable, until it become locked through the mechanical lock assembly.

In either of these two conditions, the maximum pull introduced to the main drive cable from the secondary cable of one row is that of the counterweight. Therefore, if there are 50 rows driven by one actuator and each row has a 25 lb counterweight, then an actuator capable of withstanding at least 1250 lbs will be necessary. Since the main cable is the only cable subjected to this force and it is in a straight line down the array, very little structure is required to deal with this loading. The secondary cables in this example would be subjected to no more than roughly 25 lbs.

Another important aspect mentioned is that this array is driven independently. All rows will tend to keep the weight on the roof sitting there with 25 lbs tension in their own secondary cables, but each of these rows is driven independently of each other in terms of when they “let go”. It is possible, therefore, to drive each row with a common actuator unit and single main cable, but it is not necessary to design the secondary cables and rack structure for a compounding loading due to the actuator.

Finally, the rows are highly damped to prevent high intermittent winds from messing with the tracking. The damper also removes the possibilities of the weights slamming into the roof or of the rack rotating quickly and breaking when the mechanical lock assembly locks out.

The module clamps shown and the square tube to circular housing bushings are parts that are known. The 4″ steep tube is standard. The Z channel and connection posts to attach to the roof are borrowed from a “standard rack” design. 

1. An active tracking solar assembly comprising: a main actuator cable; a secondary cable having a first end and a second end, wherein the first end is connected to the main actuator cable and the second end is connected to a roof weight; and an actuator bar having a counter-weight attached to a first end and a pulley attached to a second end, wherein the secondary cable passes through the pulley. 